Optically decentered face shield

ABSTRACT

A face protector includes a one piece shield in which an optical center is displaced away from the normal straight ahead line of sight toward an activity specific line of sight to minimize image shift that occurs when a direction of gaze passes across the edge of the shield. An apex of the shield is formed at a forwardmost point of the shield, or a virtual extension of the shield, when the shield is in an as worn position on a wearer. In particular examples, an optical axis extends through the optical center, at a non-zero angle to the normal straight ahead line of sight and substantially parallel to the activity specific line of sight, with the optical center being placed away from the apex. In particular examples, the optical axis is closer to (or coincident with) an activity specific line of sight of one of the right or left eye. The face protector is particularly useful in activities such as sports, for example hockey, football, or baseball which involve activity specific lines of sight. In one disclosed embodiment, the optical center is positioned at or below a bottom edge of the shield so that a hockey player can view an object on the ice below the lower edge of the shield with reduced image shift.

FIELD OF THE DISCLOSURE

This disclosure concerns protective shields with improved optics thatoptimize visual performance.

BACKGROUND OF THE INVENTION

There is an increasing demand for eye and face protection for people whoparticipate in sports and other activities that can potentially damagethe eyes or other facial structures. Eye injuries (sometimes leading toloss of vision) can occur in sports such as hockey and football in whichobjects (such as sticks, pucks, or another player's elbows or fingers)can strike a participant's eye or face with destructive velocity andforce. Protective shields are also used for a variety of non-sportsrelated tasks, such as mowing lawns or hammering nails, to help preventinadvertent projectiles from injuring the eye or face. An increasedawareness of the potentially infectious nature of body fluids has alsoprompted many health care professionals to wear protective eyewear orface shields when treating patients, to avoid accidental infections fromblood, saliva or other fluids splattered into the eye or on other mucusmembranes.

One drawback to the use of protective face shields is that shields candistort the wearer's vision. Early face shields were merely a flat sheetof plastic bent into an arcuate shape to conform to the facial contour.However such a shield causes significant optical distortion that can bedistracting to the wearer, and cause serious performance problem inpersons who require precise visual input, such as athletes, pilots andsurgeons.

The prior art is replete with examples of efforts to overcome opticaldistortion in protective eyewear. Rayton's U.S. Pat. No. 1,741,536(issued in 1929 to Bausch & Lomb) discloses a protective goggle in whichthe front and back surfaces of the lenses were defined by two sphereshaving offset centers. An optical centerline (optical axis) through thecenters of the spheres is spaced from, and oriented parallel to, adirect straight ahead line of sight. This optical configuration providesa tapered lens, in which the lens thickness gradually decreasessymmetrically from the optical center toward the edges. Maintaining theline of sight parallel to the optical axis helps neutralize thedistortion that would otherwise be caused by wrapping the lenseslaterally with respect to the eye.

The problem of distortion in a face shield was also addressed in U.S.Pat. No. 4,271,538 (the Montesi patent), which disclosed an opticallycorrected shield having spherical inner and outer surfaces that definedan optical center C over the bridge of the nose. The thickness of theshield tapers in all directions away from the optical center C, which isthe thickest portion of shield. As shown in Table I of that patent, thelens can have a small amount of minus power (±0.03 diopters), andminimizes viewing distortion. Since the optical centerline of thisspherical lens is through the optical center C, the optical centerlineis spaced from and parallel to the normal (straight ahead) line ofsight, as in the Rayton patent.

In the 1980s, the Foster Grant Company sold dual lens Eyeguardprotective eyewear, having a spherical lens in front of each eye withboth wrap and pantoscopic tilt. As in the Rayton patent, the opticalaxis of each lens is spaced from and maintained parallel to thestraight-ahead/normal line of sight. The optical centerline ishorizontally and vertically offset from, as well as parallel to, thenormal line of sight. The horizontal and parallel offset of these lineshelps neutralize the distortion caused by lateral wrap of the lens,while the vertical and parallel offset helps neutralize the distortioncaused by pantoscopic tilt.

A similar “optically corrected” face shield lens is shown in U.S. Pat.No. 6,010,217 which issued to Oakley, Inc. This patent discloses a faceshield having a spherical lens in which the optical centerline ishorizontally and vertically spaced from and substantially parallel tothe normal line of sight when the shield is worn. The optical axis ofthese shields passes through the apex of the shield, which is theforwardmost point of the shield in the as worn condition. Hence theoptical center of the shield is at the apex. This is the same approachthat was disclosed by Montesi as early as 1981.

U.S. Pat. Nos. 5,815,848 and 6,038,705 also issued to Oakley, anddisclose a low power “optically correct” face shield having a thickestportion at the center of the lens, from which the lens tapers in alldirections, as in Montesi's U.S. Pat. No. 4,271,538. This design wasalso used in visors of military helmets during the 1980s.

A variety of eyewear designs have also been proposed to address thevisual demands of particular sports. U.S. Pat. No. 5,614,964 disclosesdual lens eyewear, especially adapted for cycling and alpine skiing, inwhich each lens has an exterior lens surface with a single center ofcurvature. The inner radius of curvature of each of the right and leftlenses is greater than the outer radius of curvature. The centers ofcurvature of the inner spheres are also offset horizontally andvertically.

U.S. Pat. No. 5,457,502 discloses eyeglasses particularly suited for aperson who is bending forward and looking ahead, such as a bicyclist. Anupper spherical portion of the lens has a different radius of curvaturethan the lower spherical portion of the lens, to enhance visual claritywhen the cyclist is leaning forward and looking up.

U.S. Pat. No. 5,555,038 also shows spherical lenses for use in eyewear.The centers of curvature of the right and left lenses are horizontallyseparated by a distance of 0.1 to about 4.0 cm. This geometry is said tohelp ensure that the lenses fit closely over each eye without distortingor blocking vision of the wearer in the central portion of the lens.

SUMMARY OF THE DISCLOSURE

If a wearer shifts a direction of gaze such that the line of sight issignificantly not parallel to the optical axis of a lens, but stillthrough the shield, the shield will produce substantial distortion, suchthat the image is perceived to be in a different location than theactual object. This shift is even more pronounced when a wearer shifts adirection of gaze between the shield and the surroundings, producing ajump in the visual image caused by the change in refraction as the lineof gaze passes across the edge of the shield.

These problems are addressed in the present disclosure by a protectiveshield to be mounted in an as worn orientation in front of the face of awearer for a sight specific activity that involves an activity specificline of sight (ASLS) that is different than a normal straight ahead lineof sight (NLOS). The shield extends across the eyes and nose of thewearer, and has an optical axis extending through an optical center thatis substantially parallel to but shifted in the direction of the ASLS tominimize image shift as a line of gaze moves toward the ASLS. Forexample, if the ASLS is near the bottom edge of the shield, the opticalcenter is shifted toward or below the bottom edge of the shield, suchthat the optical axis is spaced from and substantially parallel to theactivity specific line of sight. This arrangement minimizes image shiftwhen the wearer's gaze is in that lower zone of the shield and if thewearer's gaze moves from the lower shield to below the shield.

In some particularly disclosed embodiments, the shield includes anarcuate face protector lens having a sight line across the shieldthrough which both of a wearer's normal straight ahead lines of sightextend when the face protector is worn. The optical axis of the shieldextends through the optical center below the sight line of the shield,for example below the apex of the shield, which is the forwardmost pointof the lens in the as worn orientation. In a disclosed embodiment, theoptical center is below the bottom edge of the lens, for example atleast 5 mm or 10 mm below the lower edge of the lens. The bottom edge ofthe lens is also the thickest edge, from which the thickness of the lenstapers. In particular embodiments the lens is a spherical lens having apower of −0.12 to +0.12 diopters, for example a zero power lens, or atoroidal lens having different radii of curvature in the horizontal andvertical planes. In other embodiments, the lens tapers symmetricallywith respect to an optical center point that is below the lower edge ofthe lens, for example below the midpoint of the lower edge. Hence athickness of the lens tapers from the lower thicker edge to the topthinner edge, and the lateral edges of the lens similarly taper from thebottom toward the top of the lens.

In particular examples, the protective shield has an optical axis thatextends through its optical center (where the optical center can be onor off the shield), and the optical axis is substantially parallel toand horizontally and vertically displaced from the ASLS of a right eyeand a left eye. In other embodiments, the optical axis is substantiallyequidistant between the ASLS of the right eye and the left eye, and in aplane that includes both the ASLS of the right eye and the ASLS of theleft eye. In yet other embodiments, the optical axis is substantiallycloser to or coincident with the ASLS of one eye compared to that of thefellow eye. In certain examples in which the optical axis is closer toone eye than the other, the optical axis is substantially parallel toand displaced laterally in the direction in which a direction of gaze isdirected. For example, if gaze is directed down and to the right, theoptical axis is substantially parallel to the ASLS of each eye, butcloser to the ASLS of the right eye than the left eye. For example,depending on the angle of the ASLS to the NLOS, the optical axis may bebetween the ASLS of the right and left eye, coincident with the ASLS ofthe right eye, or not between the ASLS of the right and left eye butstill closer to the ASLS of the right eye than the ASLS of the left eye.If gaze is directed up and to the left, the optical axis issubstantially parallel to the ASLS of each eye, but closer to the ASLSof the left eye then the right eye. For example, the optical axis may bebetween the ASLS of the right and left eye, coincident with the ASLS ofthe left eye, or not between the ASLS of the right and left eye butstill closer to the ASLS of the left eye than the ASLS of the right eye.

The shields disclosed herein generally are relatively low base lensesthat may be spherical or non-spherical (for example toroidal). Aspherical lens has a single radius of curvature that defines eachsurface, while a toroidal lens may have different radii of curvature inperpendicular meridians. For example, a toroidal lens surface may have afirst radius of curvature in a horizontal meridian and a second(different) radius of curvature in a vertical meridian. In particularexamples, the shields disclosed herein have a base curve of 2-7diopters, for example 4-6 diopters. In certain toroidal examples, theshield may have different horizontal and vertical curvatures withinthese ranges, or significant curvature in only one meridian (such as ashield that curves horizontally across the face but not vertically). Insuch an example, the base curve in one meridian (such as the verticalmeridian) may be 0-4, for example 0.

Methods are also disclosed for protecting the face of a subject bymounting the lens in front of the face, for example by attaching it to ahelmet worn by the subject. The lens is mounted in front of the face,with the optical center at or beyond the edge of the lens across whichthe line of sight moves to the activity specific line of sight. Forexample, a hockey shield lens is mounted with an optical center belowthe lower edge of the shield lens, so that a hockey player's gaze canshift between the lens and an ice surface (for example to view a hockeypuck) while minimizing image shift.

Methods are also disclosed for reducing image distortion of the shieldby cutting away peripheral portions of a molded lens. Elimination ofperipheral molded material can diminish optical distortion or image jumpthat would otherwise be encountered if the original molded material wereleft in place on the shield. It is particularly helpful to cut awayportions of the shield along edges across which the wearer's gaze passeswhen moving from a normal line of sight to an activity specific line ofsight. This method is of general use in any shield in which reduction ofperipheral distortion is desired, and it can be used to make the shieldsdisclosed herein that incorporate corrected optics, or other shieldsthat do not incorporate the corrected optics disclosed herein in whichthe optical center is aligned with the activity specific line of sight.

The foregoing and other features and advantages of the invention willbecome more apparent from the following detailed description of severalembodiments which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of the protective shield mounted to ahelmet.

FIG. 2 is an isolated front elevational view of the shield shown in FIG.1, with the position of the normal straight ahead lines of sight (andthe sight line that they intersect) illustrated schematically.

FIG. 3 is a vertical cross-sectional view of the shield along lines 3-3of FIG. 2, with the shield shown mounted to a helmet on the head of awearer, and schematically illustrating the optical axis and straightahead line of sight, as well as the apex line that extends through theapex (forwardmost point) of the shield and the front center of curvatureof the vertical centers of curvature.

FIG. 4 is an isolated view of the shield shown in FIG. 3, showing thefront and back radii of the shield in the vertical plane.

FIG. 5 is a horizontal cross-sectional view taken along line 5-5 in FIG.2, showing the front and back radii of curvature in the horizontalplane.

FIG. 6 illustrates the horizontal and vertical position of the opticalcenter in a shield designed for an activity specific line of sight. Theoptical center is vertically displaced in a vertical midline of theshield. FIG. 6A illustrates a schematic front view of the shield, FIG.6B is a side view of the shield shown in FIG. 6A, and FIG. 6C is ahorizontal section through the shield of FIG. 6B at the level of theNLOS along lines 6C-6C. The displacement of the activity specific lineof sight (ASLS) from the normal line of sight (NLOS) and apex (APX) isdepicted by arrows in FIG. 6A FIG. 6B illustrates that the optical axisis parallel to and spaced from the ASLS, and equidistant between theASLS of the right and left eyes.

FIGS. 7A-7C are schematic drawings similar to FIGS. 6A-6C, butillustrating horizontal and vertical decentration in a shield designedfor an activity specific line of sight (ASLS) that is displaced down andto the right from a normal straight ahead line of sight (NOS) and apex(APX).

FIGS. 8A-8C are schematic drawings similar to FIGS. 6A-6C, butillustrating horizontal and vertical decentration in a shield designedfor an activity specific line of sight (ASLS) that is displaced up andto the right from a normal straight ahead line of sight (NLOS) and apex(APX).

FIGS. 9A-9C are schematic drawings similar to FIGS. 6A-6C, butillustrating vertical decentration without horizontal decentration in ashield designed for an activity specific line of sight (ASLS) that isdisplaced only upwardly from the normal straight ahead line of sight(NLOS) and apex (APX).

FIG. 10A is a schematic front view of a shield, illustrating a normalline of sight plane NLOS P that extends along the sight line of theshield through the plane of the normal line of sight (NLOS) of the right(NLOS R) and left (NLOS L) eye, and the median plane MP that isequidistant between the NLOS of the right and left eyes andperpendicular to normal line of sight plane NTLOS P. FIG. 10B is aschematic view illustrating the location of the NLOS of each eye in thenormal line of sight plane NLOS P that extends through the sight line ofthe shield, and the location of the activity specific line of sightplane ASLS P that extends through the ASLS of the right eye (ASLS R) andthe left (ASLS L) eye. FIG. 10C is a perspective view of a lens blankconforming to a portion of a curved surface, showing a shield profile tobe cut from the blank in accordance with one method disclosed herein.FIG. 10D is a perspective cutaway view of the curved surface of FIG. 10Ctaken along line 10C-10C.

FIG. 11 is a schematic front view of a shield, illustrating a method forcutting away peripheral plastic material from some of the edges of theshield to improve the peripheral optical performance of the shield. Theedges of the shield that are cut away are shown in phantom.

FIG. 12 is a view similar to FIG. 10, but showing the shield cut from alarger lens blank (illustrated in phantom) that helps reduce peripheraloptical distortion of the resulting shield.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS Abbreviations

APX: Apex

ASLS: Activity Specific Line of Sight

C₁: Center(s) of curvature of front shield surface

C₂: Center(s) of curvature of rear shield surface

FP: Frontal Plane

GC: Geometric Center

L: Left, usually with reference to the left eye

MP: Median Plane

NLOS: Normal Line of Sight.

NLOS R: Normal Line of Sight of the right eye

NLOS L: Normal Line of Sight of the left eye

OA: Optical Axis

OAh: Optical Axis horizontal component

OAv: Optical Axis vertical component

OC: Optical Center

R: Right, usually with reference to the right eye

Rfh: Front surface Radius of curvature horizontal meridian

Rfv: Front surface Radius of curvature vertical meridian

Rrh: Rear surface Radius of curvature horizontal meridian

Rrv: Rear surface Radius of curvature vertical meridian

Terms

To facilitate an understanding of the terms used in the specificationand claims, some of those terms are discussed in this section.

The “normal line of sight,” which is also referred to as the NLOS, is afixed line that projects forward from each eye when the eyes are fixedon a distant point. The NLOS can refer to the line of sight of a singleeye or both eyes (because the direction of gaze is normally maintainedin the same direction by brainstem reflexes to avoid diplopia). The NLOSof the two eyes extend in a generally horizontal plane through the eyeswhen the head is in an upright position with the eyes staring into thedistance. When the head is not in the upright position the NLOS extendsin a transverse (anterior-posterior) plane of the head through the eyes.A particularly convenient way to determine a NLOS is to place eyewear ora shield on a conventional headform (such as an Alderson or Canadianhead form) which has been designed based on a statistical norm for apopulation. The position of the NLOS (or the plane that contains theNLOS of the two eyes) can be determined by reference to this headform,which can readily establish a normative position for a population.

An “activity specific line of sight” is abbreviated ASLS, and is adeterminable direction of gaze for performing a particular activity.Since the direction of gaze is yoked for the two eyes, the ASLS of eacheye is substantially parallel, or slightly convergent, in a common plane(referred to herein as the activity specific line of sight plane ASLSP). The ASLS is generally determinable for a population performing aparticular activity, such as a particular recreational or occupationalactivity.

Particular examples of an ASLS include a downward gaze for a hockeyplayer whose sight is fixed on an ice puck on a rink; a lateral gaze fora baseball player who is standing in a batting stance looking toward apitcher; and an upward gaze for a football player who is playing at aposition that requires looking up to catch a football (such as areceiver looking up at an approaching passed ball). All of theseactivities involve activity specific lines of sight that require optimalvisual performance at a time when a direction of gaze is averted from astraight ahead direction for which most protective shields (such ashockey, batting or football helmets) have optimized optical performance.

The terms “horizontal plane” and “vertical plane” refer to horizontaland vertical planes when the head is in the upright position.

A median plane (MP) is a unique plane that passes longitudinally throughthe middle of the body from front to back and divides the head intoright and left halves. A frontal plane (FP) is any one of a series ofplanes passing through the body from side-to-side, at right angles tothe median plane, or a plane that is parallel to such a plane. Somefrontal planes divide the body into front and back parts. Any frontalplane and the median plane are perpendicular to one another.

An “apex” of a shield or lens refers to a forwardmost point of theshield or lens in the as worn condition with the head in the neutralupright and straight ahead position. An apex can be on the shield orlens itself, or on a virtual extension thereof. A “virtual extension”refers to a position that would be on the shield or lens if the opticalsurfaces extended beyond the borders of the shield or lens.

The “geometric center” of a lens is the center of a rectangle thatcircumscribes each frame aperture from a frontal perspective. Thelocation of the geometric center can easily be located at theintersection of diagonals of each rectangle, or the intersection ofperpendicular bisectors of the horizontal (A) and vertical (B)dimensions. The distance between the centers (DBC) is the distancebetween the geometric centers of the two apertures of the frame. Theconcept of a geometric center can also be applied to a lens blank. Forexample, a lens blank having a circular outline has a geometric centerat the axis of symmetry of the lens blank that extends perpendicularlythrough the lens blank at its center.

“Substantially parallel” means within 15 degrees of parallel, forexample within 5 or 10 degrees of parallel, or even within 2 degrees ofparallel.

In certain examples, the optical axis is said to be parallel orsubstantially parallel to the ASLS of each eye, and closer to the ASLSof either the right eye or the left eye. The optical axis is consideredcloser to the ASLS of one of the eyes if the minimum measured distancein millimeters between the optical axis and the parallel ASLS of the oneeye is less than the minimum measured distance in millimeters betweenthe optical axis and the parallel ASLS of the other eye. The measurementof the minimum distance between two parallel lines will be evident toone of skill in the art as the length between the two parallel lines ofa line that horizontally intersects the two parallel lines.

Embodiment of FIGS. 1-5

One example of an optically improved one-piece face shield 10 is shownin FIGS. 1-5. In this embodiment, shield 10 is mounted to a helmet 12that is worn by a subject. When helmet 12 is in place on the head 14(FIG. 3) of the subject, shield 10 is held in front of the face 16 sothat the shield protects nose 18 (FIG. 3) and eyes 20, 22 (FIGS. 2 and3). In the illustrated embodiment, the shield extends through an arc ofmore than 180 degrees across the front of the face and over the temples,and from the top of the helmet, down over the forehead to between thenose and upper lip. The shield therefore protects the forehead, temples,eyes, nose and cheek bones (zygomatic arch).

Shield 10 has a lower edge 26, an upper edge 28, and side edges 30, 32.An inclined frame member 34 extends along top edge 28 and contains aplurality of perforations 36 a, 36 b, 36 c, and 36 d that form vents forshield 10 between top edge 28 and a substantially cylindrical beadededge 38 of frame member 34. Frame member 34 can either be unitary withor separate from shield 10. Two cylindrical plastic hinge members 40 aand 40 b extend from the front of helmet 12, and encircle reduceddiameter portions 41 a and 41 b of beaded edge 38 to pivotally mountshield 10 to helmet 12 in a manner that allows shield 12 to rotatebetween a fixed, protective position shown in FIGS. 1-5, to an openposition (not shown) in which shield 10 does not cover the face. A guidestop flange 44 is mounted at each temple of helmet 12 such that a topedge of side supports 46, 48 (FIGS. 1 and 5) of frame member 34 engagesstop flange 44 when shield 10 is in the desired closed (face-protecting)orientation.

The front portion of shield 10 forms a clear one-piece lens 50 thatextends below frame member 34 across the eyes and nose, between sidesupports 46, 48. The junction between lens 50 and side supports 46, 48is illustrated in FIG. 5, at which point the thickness of shield 10substantially thickens. Lens 50 can have a variety of opticalconfigurations, such as spherical, cylindrical, toroidal, or aspheric,and is preferably made of plastic of sufficient thickness to provideadequate protection of the face from impact. The disclosed embodiment oflens 50 is of non-uniform thickness, and it tapers across its height andwidth from a center thickness CT point that may be on or off the lens.In the illustrated embodiment, lens 50 excludes the frame portion ofshield 10 (such as frame member 34 and side supports 46, 48) and lens 50is itself toroidal as shown in FIGS. 3-5.

In a preferred embodiment, lens 50 has a front surface 52 that conformsto the surface of a torus having front centers of curvature 54 h and 54v (FIGS. 4 and 5) with respective front radii of curvature Rfh (in thehorizontal plane) and Rfv (in the vertical plane), and has a rearsurface that conforms to the surface of a torus having rear centers ofcurvature 58 h and 58 v (FIGS. 4 and 5) with rear radii of curvature Rrh(in the horizontal) and Rrv (in the vertical). In the sphericalembodiment of the lens, Rfh and Rfv are equal, centers of curvature 54 hand 54 v are coincident, Rrh and Rrv are equal, and centers of curvature58 h and 58 v are coincident. In a plane cylinder embodiment of thelens, the corresponding front and rear radii of curvature in onemeridian are infinite in length.

If the corresponding front and rear centers of curvature of a curvedlens are coincident, this relationship of the front and rear surfaceswould produce a lens having minus power. In examples in which lens 50has zero power, the desired radii of curvature can be determined usingthe lens power equation. Similarly, a lens having a small amount of lenspower can be provided. In the particularly disclosed embodiments, thelens is a non-corrective lens having a dioptric power (plus or minuspower) of less then 0.25 diopters, and in particular less then 0.12dipoters. In especially preferred examples, the power of the lens isless than 0.06 diopters.

As best shown in FIG. 3, shield 10 is mounted in front of the face of awearer such that it intersects a NLOS 60 of the wearer. The NLOS 60 foreach eye intersects lens 50 along a transverse sight line 61 (FIG. 1) oflens 50, that extends from side to side across the lens in a transverseanatomical plane that would intersect the head of the wearer. Sight line61 therefore lies in a NLOS plane that includes the normal lines ofsight of both eyes 20, 22. Each NLOS 60 extends through the center ofrotation of the eye and the pupil, along a sight line of a personlooking straight ahead into the distance.

An optical axis 62 (FIG. 3) of the lens extends through the centers ofcurvature of the front and rear surfaces 52, 56 of lens 50. In a sphereor plane cylinder, the optical axis extends through the two centers ofcurvature of the front and rear surface meridians that are curved. In aspherocylinder, the optical axis extends through the center of curvatureof the spherical surface and the two centers of curvature of theprincipal meridians of the cylindrical surface. In a toroid, the opticalaxis extends through the four centers of curvature of the principalmeridians of the front and rear surfaces. It is well understood by thoseskilled in the art that any of these surfaces in these embodiments alsomay be generated with aspheric curvatures.

The parameters of lens 50 that contribute to its optical performanceinclude surface curvatures, separations of centers of curvature, centerthickness, and material index of refraction. Practical considerations inthe lens design include such factors as relative impact resistance,minimum thickness requirements, lens position and orientation withrespect to the wearer, field of view requirements for the wearer, facialmorphology of the wearer, and lens carrier system (e.g., helmet, goggle,spectacle). For example, a non-corrective plastic lens designed for useas an occupational protective face shield conforming to ANSI standardsmust have a minimum thickness at any lens location of 1 mm. In anotherexample, a non-corrective lens designed to be worn as a hockey faceshield mounted to a helmet will have a horizontal curvature of about 5-6diopters and a vertical curvature of about 2-3 diopters. In yet anotherexample, a lens manufactured from CR-39 or acrylic, both with refractiveindices of about 1.5, would require different surface curvatures andcenter thickness compared to a lens manufactured from polycarbonate,with refractive index of about 1.59, to produce a final lens withequivalent total power. Table 1 demonstrates examples of possibleembodiments based on particular requirements of parameters and allowabletolerances. These examples are meant to illustrate specificapplications, and are not meant to limit the invention.

TABLE 1 Sample values and tolerances for several different embodimentsof the invention. Baseball (right- Parameter Hockey Football handedbatter) center thickness, mm 3.76 3.11 3.76 index of refraction 1.591.59 1.59 meridian Horizontal Vertical Horizontal Vertical Horizontal &Vertical front surface curvature, mm 94.8 187.4 106.0 192.7 176.7 Rearsurface curvature, mm 93.4 186.0 104.85 191.55 175.3 total power,diopters 0 0 0 0 0 angle between lens optical 0 OA 15 deg 0 OA 15 OA 30deg left of axis (OA) and wearer's below deg above NLOS normal line ofsight (NLOS) NLOS NLOS total power tolerance, ±0.12 ±0.12 ±0.12 ±0.12±0.12 diopters separation of front and rear 2.36 2.36 1.96 1.96 2.36centers of curvature, mm

An alternate or additional application could result in a different orgreater angle between the shield optical axis and the wearer's normalline of sight. For example, a shield for a left-handed baseball battercould incorporate an optical axis 30 degrees to the right of the normalline of sight. Likewise, a shield for luge participants couldincorporate an optical axis 45 degrees below the normal line of sight.Similarly, a shield for skeleton participants could incorporate anoptical axis 40 degrees above the normal line of sight.

With the helmet in place on the wearer, and the head and eyes in theposition they would assume for the normal lines of sight, lens 50 has anapex 66 (FIGS. 2-4) which is the forwardmost point of the shield lensthat would first come into contact with a frontal plane as the shieldlens approaches the frontal plane when the head is held in an upright orneutral position. The frontal plane is perpendicular to the normalstraight-ahead lines of sight; hence the frontal plane FP is a verticalplane, which is shown in FIGS. 3-4 tangent to the apex of the lens,where the apex 66 of the lens is located below the lines of sight, andhalfway between the lines of sight. In this embodiment, the shield hasreverse (or negative) pantoscopic tilt. In other embodiments, the shieldmay have positive or even no pantoscopic tilt. Pantoscopic tilt (eitherforward or reverse) can be used to improve face coverage, clearance andfit. However, regardless of any tilt that is chosen, the optical centerOC will for example be below the apex in a hockey shield which is wornby a player looking down toward the ice rink surface, or above the apexfor a skeleton participant lying prone who is looking toward an upperedge of the shield while participating in competition. The opticalcenter is displaced from the apex in the same direction that theactivity specific line of sight is displaced from the normal straightahead line of sight. Hence in a shield to be worn for an activityspecific line of sight that is up and to the right from the normal lineof sight, the optical center of the shield is displaced up and to theright of the apex of the shield. The distance by which the opticalcenter is displaced in this manner is preferably proportional to thedistance by which the activity specific line of sight is displaced fromthe normal line of sight, although non-proportional displacement canalso achieve a degree of noticeable optical correction.

As illustrated in the embodiment of FIG. 3, the vertical centers ofcurvature 54 _(v), 58 _(v) are arranged with respect to one another suchthat optical axis 62 extends through them at an angle θ_(v) to thenormal line of sight 60. The direction of deviation of optical axis 62away from the normal line of sight 60, and the value of angle θ_(v),depends on the particular use for which the shield is intended. In someembodiments, optical axis 62 is downwardly inclined below the plane ofthe normal line of sight 60 (the plane through sight line 61 thatincludes the normal lines of sight of both eyes), for example at orbelow apex 66. The optical center is the point at which the optical axisintersects the lens, or intersects an imaginary (virtual) extension ofthe lens. Displacement of the optical center away from the apex isreferred to as optical decentration, and such optical decentration canoccur either in the horizontal plane (for example toward or away fromthe nose), in the vertical plane (for example toward the top of the heador the chin), or in both planes (for example an optical center at thebottom lateral edge of the lens).

For the hockey shield illustrated in FIGS. 1-5, optical axis 62 extendsin the vertical midline of the lens (a vertical line of symmetry of thelens) but is inclined downwardly to the plane of the normal line ofsight 60 by an angle of about (or at least) 15 degrees with respect tothe normal line of sight, such that it is below apex 66, and does noteven intersect lens 50 but instead extends below lower edge 26 of lens50. This arrangement provides an optical center 68 that is located on animaginary extension of lens 50, below lower edge 26. In this position,the optical center will produce minimal image shift as the wearer's lineof sight moves from below lens 50 and into the lens itself. Thereduction of the image shift is of particular advantage for someone whoshifts a line of sight between normal line of sight 60 and an activityspecific line of sight below shield 10 (such as a line of sight a hockeyplayer may use to view a puck on the surface of an ice rink).

In use, helmet 12 is placed on the head of a wearer, with the shield inthe closed position so that lens 50 extends over and protects the eyesand nose of face 16 in the as worn orientation of the shield. Vents 36a, 36 b, 36 c and 36 d provide for air circulation through the spacebetween face 16 and shield 10 to help minimize fogging of lens 50.Shield 10 can also be rotated to an open position by lifting up itslower edge 26 to pivot lens 50 away from the face around hinges 40 a, 40b.

When shield 10 is in the closed position, a hockey player is able toshift gaze from looking through the lens to below the lens, whileminimizing image shift that occurs as the line of sight passes over thisinterface. The amount of image shift will be proportional to thedistance between the sight specific line of sight (such as looking at ahockey puck on the surface of an ice rink) and the position of theoptical center. Hence an optical center positioned below the lower edgeof lens 50 will produce substantially less image shift than similarlenses in which the optical center is located at the apex, or at thelevel of the NLOS.

Although the particular example illustrated in the drawings is a hockeyshield, the principles of the invention can be extended to many othertypes of shields to minimize the spatial distortion when the activityspecific line of sight is located on the lens but not coincident withthe normal line of sight, as well as the image shift that occurs whenthe line of sight crosses from the lens edge. For example a surgeon mayhave a protective face mask that covers the eyes and nose but not therest of the face. In those instances in which the primary visualactivity for the surgeon is toward the lower edge of the shield, and insome cases when the line of sight shifts between the lens and below it,optical advantages are provided by vertical decentration of the lens toor below the lower edge of the lens. Particular examples of decentrationalong a vertical midline include a decentration of at least 10, 20 or 30mm from the lens apex. Decentration of this or any other lens may occureither in the vertical midline of the lens (halfway between the twolines of sight), or away from the vertical midline of the lens

In another example, the optical center may also be horizontallydecentered, such that it is not equidistant between the two eyes. Thistype of shield may be intended for use with laterally-displaced specificactivity lines of sight, such as baseball batting and short-track speedskating. A baseball batter, for example, stands somewhat sideways to thepath of a thrown baseball with the head at an angle that results in asideways gaze, and often an upward gaze as well. The horizontallydecentered optical center may be, for example, nearer the activityspecific line of sight toward which the direction of gaze is directed.For example, if the activity specific line of sight is laterallydisplaced toward the right of the NLOS, then the optical center may bepositioned closer to the activity specific line of sight of the righteye than the left eye (and in certain embodiments the optical center mayeven be coincident with the activity specific line of sight of the righteye).

In yet another example, a football player will have an activity specificline of sight predominantly in an upward direction, such that theoptical center may be near or above the upper edge of the shield. Suchan upward line of sight would be used, for example, when standing information prior to a play. Different players in a game (such asdefensive linemen and wide receivers in a football game) may havedifferent activity specific lines of sight, such that different shieldsare suitable for different players on the same team. The activityspecific lines of sight for a particular game (or for participants in agame who are performing a function) may be determined for eachindividual player or fixed for a particular game or class of player.

In yet other examples, the activity specific line of sight is bothvertically and horizontally displaced from the normal line of sight,such that the optical center is both vertically and horizontallydisplaced from the apex of the shield. In disclosed embodiments, theoptical axis is horizontally and vertically displaced from the NLOS andthe ASLS, and substantially parallel to the ASLS (for example, within 5or 10 degrees of parallel). In specific embodiments, the optical axis issubstantially equidistant between the ASLS of the right and left eyesbut in other embodiments is not equidistant therebetween. For example,the optical axis (and optical center) may be vertically displaced fromthe apex in a direction that corresponds to a vertical component ofgaze, in that the optical axis is displaced downwardly from the apex ifthe direction of gaze is downward from the NLOS. Similarly, the opticalaxis may be between the ASLS of the right and left eyes, but closer tothe eye toward which a horizontal component of gaze is directed.Alternatively, the optical axis may be coincident with the ASLS of theeye toward which the horizontal component of gaze is directed, or haveshifted beyond the ASLS of the eye toward which the horizontal componentof gaze is directed, so that the optical axis is no longer between theASLS of the right and left eye. For example, if the direction of gazehas a horizontal component that is directed toward the left, then theoptical axis is closer to the ASLS of the left eye than the ASLS of theright eye. In particular examples, the optical axis may be between theASLS of the right and left eye, coincident with the ASLS of the lefteye, or shifted beyond the ASLS of the left eye such that the opticalaxis is not between the ASLS of the right and left eye.

Designing Shield with Specific Lens Power and Pantoscopic Tilt

By convention, the curvature of the front surface of a lens is calledthe base curve and is defined as 530/R₁, where R₁ is the radius ofcurvature of that surface in millimeters. A line through the centers ofcurvature C₁ (of the front surface) and C₂ (of the rear surface) definesan optical axis OA that intersects the lens (or an imaginary extensionof the lens) at an optical center OC. The lens (or its imaginaryextension) has a thickness CT along the optical axis OA, and taperssymmetrically away from or towards the optical center OC (depending onthe power of the lens). The radius of curvature R₂ of the rear surfaceis selected in combination with the center thickness CT and the basecurve radius R₁ to provide a predetermined lens power. The radius R₂ fora selected lens power P is readily calculated using the standard formulafor lens power:

$P = {\left( {n - 1} \right)\left\lbrack {\frac{1}{R_{1}} - \frac{1}{R_{2}} + \frac{\left( {n - 1} \right)C\; T}{n\; R_{1}R_{2}}} \right\rbrack}$wherein n is the refractive index of the lens material.

Pantoscopic tilt may be defined as the angle between the apex plane (theFP shown in FIGS. 3 and 4, which is perpendicular to the normal lines ofsight of the right and left eyes) and the tangent to the lens surface atthe intersection of the lens surface and the normal line of sight. Theshield disclosed herein can have pantoscopic tilt (inclined toward theface), reverse pantoscopic tilt (inclined away from the face), or nopantoscopic tilt. Depending on the amount and direction of pantoscopictilt and the horizontal and vertical dimensions of the shield, the apexmay be present on the lens surface or it may be off the lens surface,such that it can be located by virtual extension of the lens surface.

Determining Activity Specific Line of Sight (ASLS)

The line of sight will often change depending on the task a person isperforming. This task specific line of sight is referred to herein as anactivity specific line of sight (ASLS). The ASLS is the line along thefixation axis of the eye when the eye and head are directed in apreferred position for performing a particular visual function or task(e.g. playing ice hockey, trail running, volleyball, surgery, baseballbatting, or driving). In trail running, for example, the eye may berotated such that the visual fixation axis through the center of thepupil is lowered about 15 degrees below the normal straight ahead lineof sight. Although the visual fixation axis for different activities isnot always constant, there is a preferred line of sight that is adoptedfor specific activities, and for which a lens can be designed.

There are several approaches to determining the ASLS. A population ofpersons performing a task can be observed performing the task, and eachof their lines of sight marked on the lenses of eyewear or shields theyare wearing (or photographs taken of the pupils through the lenses) toarrive at a norm for the ASLS. Alternatively, infrared pupil positiondetectors can be worn by persons performing the tasks, and the pupilpositions determined remotely. In addition, video analysis of head andbody position can be performed. The ASLS can be determined for anindividual (if a custom protective shield is being made), or an averageposition of the ASLS can be determined for a population of persons whoperform the activity. The lens or shield can then be worn by personsperforming the function for which the lens or shield is designed, andrefinements made to the position of the optical axis based on the visualperformance and comfort of the wearer. Since the eyes may converge aspart of an accommodative reflex if the activity involves closeractivity, the plane of the ASLS can be determined as a reference planethat includes the ASLS of the right and left eyes (referred to herein asthe ASLS plane). In examples in which the ASLS is straight up orstraight down from the neutral straight ahead position, the opticalcenter OC is preferably placed equidistant between the lines of sight ofthe two eyes.

The ASLS can be in the vertical midline of the shield (substantiallyequidistant between the eyes), or away from that vertical midline(toward one of the eyes). The ASLS can also be above or below the planethat contains the normal lines of sight of the wearer. In particularembodiments, the ASLS is both horizontally and vertically displaced fromthe normal straight ahead line of sight.

Once the angle between the ASLS (or the ASLS plane) and the normalstraight ahead line of sight (or the plane that contains both NLOS) isdetermined for the particular sport or activity, whether for anindividual or a population, this sets the angle between the optical axisof the shield and its apex (when the head and eyes are in a positionthat would define the normal line of sight).

In particular embodiments, the shield has a functional apex defined bythe tilt of the head and body position of the wearer. A functional apexis a forwardmost point on a lens that first touches a plane advancingtoward the shield perpendicular to the functional line of sight.

Placement of Optical Center

In many embodiments it is useful for the optical center to be on avertical meridian of the lens, halfway between the straight ahead linesof sight of the two eyes. Hence for an example in which the activityspecific line of sight is straight down from the normal straight aheadline of sight, the optical center is decentered downward the same angleas the activity specific line of sight and the decentration occurs alongthe vertical meridian, such that the horizontal offset of the opticalcenter from each line of sight is substantially equal for both eyes. Inother embodiments in which both horizontal and vertical decentration isdesired to accommodate an activity specific line of sight, for example,which may be down and to the right, or up and to the left, thedecentration moves the optical center in the same direction as theactivity specific line of sight, along both the vertical and lateralmeridians. In particular examples, the position of the decenteredoptical axis remains substantially parallel to the activity specificline of sight of each eye, and is either substantially equidistantbetween the ASLS of each eye (for example when the ASLS is eitherstraight up or down from the NLOS) or closer to the ASLS of the right orleft eye (for example when the ASLS is directed laterally from theNLOS). In certain examples in which the ASLS is directed laterally fromthe NLOS, the optical axis is closer to (including coincident with) theASLS of the eye toward which the ASLS is directed (for example closer tothe ASLS of the right eye if the ASLS is laterally directed toward theright). As used herein, references to right, left, up and down are thedirections with reference to the person who is wearing the shield.

Some additional examples of decentration for different activity specificlines of sight in a shield 70 are shown in FIGS. 6-9, which helpillustrate the horizontal and vertical placement of the optical centerin these situations. FIG. 6, for example, shows an activity specificline of sight that is displaced directly vertically downward, withoutsubstantial deviation to the right or left. The direction ofdisplacement of the visual axis is shown schematically in FIG. 6A by thedownwardly pointing ASLS arrows R (for the right eye) and L (for theleft eye). If the activity specific line of sight (ASLS) is broken intoa horizontal and a vertical component, the vertical component of theASLS is displaced downwardly (as shown in FIG. 6B) at an angle θ_(v) tothe normal straight ahead line of sight (NLOS) and the horizontalcomponent (shown in FIG. 6C) remains substantially parallel (for examplewithin ±5 degrees, for example within ±2 degrees) to the NLOS. In thissituation, the lens is designed with the optical center OC in the medianplane MP substantially equidistant between the NLOS of each of the rightand left eyes. The median plane may, in some examples, be a verticalplane that bisects the shield into symmetric halves. In FIG. 6, theoptical axis OA extends through an optical center at point OC that is inthe median plane, on an imaginary extension of the shield, such that thehorizontal angle of deviation of the optical axis is at an angle θ_(h)of substantially zero to the NLOS, and the vertical component of theoptical axis is at the angle θ_(v) to the NLOS. The angle of downwardangular deviation may be, for example, 5-15 degrees or more from thestraight ahead normal line of sight (NLOS). The optical axis extendsthrough centers of curvature 54 _(v) and 58 _(v) in the median plane (asshown in FIG. 6B) to provide the vertical curvature of the shield lens,and through the centers of curvature 54 _(h) and 58 _(h) in thehorizontal (as shown in FIG. 6C) to provide the horizontal curvature ofthe shield lens. As previously noted, the centers of curvature may bedifferent for the vertical and horizontal curvatures of the lens for anon-spherical lens, but for purposes of simplification a front center ofcurvature (C₁) and a rear center of curvature (C₂) are illustrated inFIG. 6A.

The apex APX is also shown in FIG. 6. As already noted (and shown in thedrawing), the apex APX is the forwardmost point of the shield when theshield is mounted in front of the eyes in the as worn orientation, withthe head upright. Also, the line perpendicular to the front surface atthe apex APX, or apex line, is parallel to the normal lines of sight ofboth eyes and intersects front vertical center of curvature 54 _(u).Consequently, the downwardly inclined optical axis OA will intersectboth the apex line and the normal line of sight with the same angle (asshown in FIG. 6B). FIGS. 6A-6C show that the optical axis of the shieldis decentered by displacement of the optical center from the apex APX.In the disclosed example, the optical center OC is decentered onlyvertically downward from the apex APX, while remaining in the medianplane MP. In particular examples, the optical center OC is movedvertically downward from the apex APX by 10 to 30 mm, for example 20 mm.The illustrated optical axis OA is spaced from and substantiallyparallel to each ASLS (and the ASLS plane). In this example, opticalaxis OA is displaced downwardly from the ASLS plane, but is equidistantbetween the ASLS of each eye and extends in the median plane MP.

FIG. 7 illustrates an ASLS in which the visual axis of each eye is bothdepressed below the NLOS and deviated to the wearer's right. Thedirection of displacement of the visual axis is shown schematically inFIG. 7A by the arrows R (for the right eye) and L (for the left eye)that are pointing down and to the right. If the activity specific lineof sight (ASLS) is broken into horizontal and vertical components, thevertical component of the ASLS (shown in FIG. 7B) is displaceddownwardly at an angle θ_(v) to the NLOS and the horizontal component(shown in FIG. 7C) is displaced horizontally at an angle of θ_(h) to thenormal straight ahead line of sight. The optical axis (which extendsthrough the centers of curvature C₁, with components 54 _(h) and 54_(v), and C₂, with components 58 _(h) and 58 _(v), of the shield lens70) is similarly angled vertically to both the normal line of sightplane and the apex line by an angle θ_(v) that is the same as thevertical component of the angle of deviation of the ASLS from the NLOS(FIG. 7B), and angled horizontally to both the median plane and the apexline by the angle θ_(h) that is the same as the horizontal component ofthe angle of deviation of the ASLS from the NLOS. In FIG. 7, the opticalaxis extends through centers of curvature C₁ and C₂, and through anoptical center at point OC that is to the right of the median plane MPof the shield, on an imaginary extension of the shield, and below thelower edge of the shield. The angle of downward displacement θ_(v) maybe, for example, 5-15 degrees or more, and the angle of horizontaldisplacement θ_(h) may similarly be 5-15 degrees or more. The opticalcenter is also moved away from the apex APX in the same directions (downand to the right) as the direction of deviation of the ASLS from theNLOS. In particular examples, the downward displacement of the opticalcenter OC from the apex APX is 10-30 mm, and the lateral displacement is10-30 mm from the apex APX.

The vertical placement of the OA can be determined, for example, bydrawing the OA substantially parallel to each ASLS, through the frontcenter or centers of curvature of the shield. Hence for the verticalcurvature (FIG. 7B), the OA placement is determined by orienting the OAsubstantially parallel and spaced from the ASLS plane, with the OAextending through point 54 v. For the horizontal curvature, the OAplacement is determined by orienting the OA substantially parallel andspaced from each ASLS, with the OA extending through point 54 h. Thepositions of the rear centers of curvature (58 v, 58 h) can bepositioned to achieve this orientation of the OA, while keeping thefront centers of curvature (54 v, 54 h) fixed.

FIG. 8 illustrates an ASLS in which the visual axis of each eye is bothelevated above the NLOS and deviated to the wearer's right. Thedirection of displacement of the visual axis is shown schematically inFIG. 8A by the ASLS arrows R (for the right eye) and L (for the lefteye) that are pointing up and to the right. If the activity specificline of sight (ASLS) is broken into a horizontal and a verticalcomponent, the vertical component of the ASLS (shown in FIG. 8B) isdisplaced upwardly at an angle θ_(v) to the NLOS and the horizontalcomponent (shown in FIG. 8C) is displaced horizontally at an angle ofθ_(h) the normal straight ahead line of sight. The optical axis OA isalso angled vertically to both the normal line of sight plane and theapex line by an angle θ_(v) that is the same as the vertical componentof the angle of deviation of the ASLS from the NLOS (FIG. 8B), andangled horizontally to both the median plane MP and the apex line by theangle θ_(h) that is the same as the horizontal component of the angle ofdeviation of the ASLS from the NLOS. In FIG. 8, the optical axis extendsthrough an optical center at point OC that is to the right of the medianplane MP of the shield, above the equator of the lens, but below theupper edge of the shield. The angle of upward displacement θ_(v) may be,for example, 5-15 degrees or more, and the angle of horizontaldisplacement θ_(h) may similarly be 5-15 degrees or more. In certainembodiments, the optical center OC is above the top edge of the shieldlens. The optical center OC is displaced in the same directions (up andto the right). In particular examples, the upward displacement of theoptical center OC from the apex APX is 10-30 mm, and the lateraldisplacement is 10-30 mm from the apex APX.

FIG. 8 also illustrates that the OA is horizontally and verticallyspaced from, and substantially parallel to, the ASLS plane. The OAshifts closer to the ASLS (while remaining substantially parallel to it)proportional to an increasing angle of vertical deviation of the ASLS tothe NLOS. The OA may be, for example, between the NLOS and ASLS,coincident with or at the same level as the ASLS, or above the ASLS.Similarly, the OA moves closer to the ASLS of the right eye than theleft eye (while still substantially parallel to the ASLS of both eyes)since the direction of gaze is shifted to the right. The OA moves closerto the ASLS of the right eye proportional to the increasing horizontalangle of the ASLS from the NLOS, and may be coincident with the ASLS ofthe right eye or to the right of the ASLS of the right eye, depending onhow large the horizontal angle is between the NLOS and the ASLS. If thedirection of gaze were directed to the left from the NLOS, then the OAwould move closer to the ASLS of the left eye proportional to anincreasing angle between the ASLS and the NLOS, while maintaining itssubstantially parallel spaced relationship from the ASLS. The ASLS maybe coincident with the ASLS of the left eye or to the left of the ASLSof the left eye, depending on how large the horizontal angle is betweenthe NLOS and the ASLS.

FIG. 9 shows an activity specific line of sight that is displaceddirectly vertically upward, without deviation to the right or left, butin which the ASLS extends through the shield and not above it. Thedirection of displacement of the visual axis is shown schematically inFIG. 9A by the upwardly pointing arrows R (for the right eye) and L (forthe left eye). If the activity specific line of sight (ASLS) is brokeninto a horizontal and a vertical component, the vertical component ofthe ASLS is displaced upwardly (as shown in FIG. 9B) at an angle θ_(v)to the normal straight ahead line of sight (NLOS) and the horizontalcomponent (shown in FIG. 9C) remains substantially parallel (within ±5degrees, for example within ±2 degrees) to the NLOS. In this situation,the lens is designed with the optical center OC in a median plane MPequidistant between the ASLS of each of the right and left eyes. Themedian plane MP may, in some examples, be a vertical plane that bisectsthe shield into symmetric halves. In FIG. 9, the optical axis OA extendsthrough an optical center at point OC that is in the median plane MP ofthe shield and on the shield, such that the optical axis is at an angleθ_(h) of substantially zero to the median plane MP, and at the angleθ_(v) to both the NLOS and the apex line. The angle of upwarddisplacement may be, for example, 5-15 degrees or more from the straightahead line of sight (NLOS), or the normal line of sight plane thatcontains the NLOS of the right and left eyes. The optical center isdisplaced in the same direction (upward only). In particular examples,the upward displacement of the optical center OC from the apex APX is10-30 mm.

As can be seen in the examples of FIGS. 6-9, the optical center isplaced in a location such that the optical axis extends through theoptical center at an angle to the NLOS plane (NLOS P), and substantiallyparallel to the ASLS of the right and left eyes.

FIGS. 10A and 10B show the NLOS plane (NLOS P) that contains the NLOS ofthe right and left eyes, and the ASLS plane (ASLS P) that contains theASLS of the right and left eyes. To provide a shield that compensatesfor the optical demands of an ASLS, the placement of the OC (and theoptical axis that extends through the OC) can be determined by thedeviation angle of the ASLS from the NLOS. FIG. 10B illustrates an ASLSP that has a horizontal component that is at an angle θ_(h) to NLOS Pand a vertical component that is at an angle θ_(v) to the NLOS P. Incertain examples, at least one of the horizontal or vertical anglesθ_(h) or θ_(v) is greater than about 5 degrees, for example at least 10,15 or 20 degrees.

FIG. 10C is a schematic view of a lens blank 82 having a circularperipheral outline conforming to a curved surface 84 from which lensblank 82 is cut. Curved surface 84 can be either spherical or toroidal,or another shape suitable for visors or shields. However, the specificsurface 84 illustrated in FIG. 10C is intended to be a toroidal surface.Lens blank 82 has a geometric center GC at the center point of lensblank 82, and a vertical meridian VM bisects lens blank 82 intosymmetric right and left halves. The profile of shield 80 is shown onlens blank 82, and the location of the optical center OC is positionedbelow the NLOS of the right eye (NLOS R), below the lower edges of theprofile of shield 80, and away from the vertical meridian VM. In theillustrated embodiment, optical center OC is located to the right ofvertical meridian VM (as viewed by the wearer of the shield).

FIG. 10D is a cutaway view of FIG. 10C along line 10D-10D (which extendsthrough the NLOS of each eye). The normal line of sight plane NLOS Pthat contains the NLOS R of the right eye and NLOS L of the left eye isillustrated schematically in the figure

In particular embodiments, the shield is cut from a decentered lensblank (such as lens blank 82) having an optical center OC that is spacedfrom the geometric center GC of the lens blank in at least a horizontaldirection from vertical meridian VM or a vertical direction fromhorizontal plane HP, or both. In this manner, the shield has an opticalaxis that extends at a non-zero angle to the normal line of sight of theright and left eye in at least a horizontal or a vertical plane, or inboth the horizontal and vertical planes. The optical axis is maintainedsubstantially equidistant between the activity specific lines of sightof each the right and left eyes, such that the optical axis is notparallel to the normal lines of sight in at least one of a horizontal orvertical plane, or in both the horizontal and vertical planes.

Diminishing Peripheral Distortion

It has been found that peripheral distortion near the edge of a faceshield lens while looking through the lens, as well as image shift thatoccurs when the line of sight passes across the edge of the lens, can beinduced by distorted peripheral optical surfaces in a molded-to-shapelens. For example, one problem with injection molded lenses or lensblanks is that there are often injection molding artifacts peripherallyin the lens, for example at the injection gate where plastic is injectedinto the lens cavity prior to hardening or with plastic flow turbulencenear the edges of the lens cavity. Such peripheral distortion can bereduced by cutting away at least some of the edges of the shield.Optical material from all the edges of the entire shield, just one ormore edges, or even portions of one or more edges, can be eliminated toimprove the optical performance of the shield. In some embodiments ofthe shield that are designed for an ASLS that passes over a singleinterface edge of the shield (such as the lower or upper edge) as thevision shifts from the NLOS, only the peripheral plastic along that edgeof the shield is cut away from the final shield.

One example of a method of making a face shield 100 is shown in FIG. 11,wherein the face shield 100 is for example made in accordance with thedesign already described in connection with FIGS. 1-9. However, theshield 100 can also be a conventional face shield that does not have theoptical design described herein for reducing optical distortion and/orshift at the periphery of the shield. Shield 100 can be obtained from aninjection molded lens blank 102 that is slightly larger than shield 100,for example having excess plastic El at the top edge 104 and E2 at thebottom edge 106, but not at side edges 108, 110. The excess plastic E1,E2 or both E1 and E2 can be cut from the shield to provide shield 100with its finished shape shown in FIG. 11, in which the shield is cut tobe mounted in an orientation that holds it in a desired relationship tothe normal lines of sight R and L of the right and left eyes (wherepoints R and L indicate the points at which each normal line of sightintersects shield 100), or in a desired relationship to the activityspecific lines of sight ASLS. The finished shape has a reduced heightcenter portion having a height hi that is less than the maximum heighth₂ of the right and left eye portions of shield 100. Lens blank 102 (andresulting shield 100) can be injection molded to any desired shape, forexample to produce a spherical or toroidal lens.

An alternative example of the method of manufacturing a face shield 111is shown in FIG. 12, in which the face shield 111 is cut from a circularoutline lens blank 112 that has been molded to the desired optical shape(such as a lens blank for a spherical or toroidal lens) having adecentered optical center OC. Face shield 111, once cut from lens blank112, has upper edge 114, lower edge 116, right edge 118 and left edge120. The optical center OC of the lens blank is “decentered” in thatoptical center OC is located at a different position on the lens blankthan geometric center GC. In the disclosed example, the OC is located onthe lens blank below the location from which lower edge 116 of shield111 is to be cut, as in the design described in association with FIGS.6A-6C. Hence cutting shield 111 from this location produces a faceprotector in which the OC is positioned in the desired location, in theplane of a vertical bisector through GC and OC that divides lens 111into symmetric halves.

In the embodiment of FIG. 12, lens blank 112 has sufficient dimensionsthat shield lens 111 can be cut from entirely within the circularoutline of lens blank 112, at a location that is interior to the edgesof lens blank 112. Hence none of the edges of shield 111 coincide withthe edges of lens blank 112, which eliminates from shield 111 theperipheral optical distortions that are often found in a lens blank. Inthe illustrated embodiment of FIG. 11, top and bottom edges 114, 116 arecut further from the edges of lens blank 112 than side edges 118, 120which provides ever greater optical performance (and less moldinginduced distortion) for the upper and lower edges than for the sideedges. Cutting shield 111 in this manner optimizes optical performanceat the top and bottom edges of shield 111, and would be preferred for ashield that is designed for an ASLS that is above or below shield 111,or in which the ASLS crosses the top or bottom edge when moving from theNLOS.

As in FIG. 12, center height h, of shield 111 is less than the maximumheight h₂ of shield 111 in the right and left eye portions. Shield 111is also cut from lens blank 112 at a position that is selected relativeto the NLOS of the right eye R and the left eye L.

In view of the many possible embodiments to which the principles of theinvention may be applied, it should be recognized that the illustratedembodiment is only a preferred example of the invention and should notbe taken as a limitation on the scope of the invention. Rather, thescope of the invention is defined by the following claims. We thereforeclaim as our invention all that comes within the scope and spirit ofthese claims.

1. A protective shield for mounting in front of a face of a wearer in anas worn orientation, with the shield extending across the eyes and noseof the wearer for use in specific activity involving an activityspecific line of sight different than a straight ahead normal line ofsight, the protective shield comprising: an arcuate lens that, in the asworn orientation, curves across the eyes and nose of the wearer, thelens having an optical center and an apex, either or both of which canbe on or off the lens, and a lower edge, and an optical axis thatextends through the optical center and the optical axis is substantiallyparallel to an horizontally displaced from the activity specific line ofsight of a right eye and a left eye, but not vertically displaced fromthe activity specific line of sight of the right eye and the left eye,wherein the optical center of the lens is displaced from the apex to aposition that reduces object shift as the wearer shifts gaze from thenormal straight ahead line of sight to the activity specific line ofsight, and the optical axis is not substantially equidistant between theASLS of the right eye and the left eye, but is closer to the ASLS of aneye toward which a direction of gaze is directed.
 2. A protective shieldfor mounting in front of a face of a wearer in an as worn orientation,with the shield extending across the eyes and nose of the wearer for usein a specific activity involving an activity specific line of sightdifferent than a straight ahead normal line of sight, the protectiveshield comprising: an arcuate lens that, in the as worn orientation,curves across the eyes and nose of the wearer, the lens having anoptical center and an apex, either or both of which can be on or off thelens, and a lower edge, and an optical axis that extends through theoptical center, and the optical axis is substantially parallel to andhorizontally displaced from the activity specific line of sight of aright eye and a left eye, but not vertically displaced from the activityspecific line of sight of the right eye and the left eye, wherein theoptical center of the lens is displaced from the apex to a position thatreduces object shift as the wearer shifts gaze from the normal straightahead line of sight to the activity specific line of sight, and thenormal lines of sight of the right and left eye extend in a normal lineof sight plane, and a median plane extends perpendicular to the normalline of sight plane equidistant between the normal lines of sight of theright eye and the left eye, and vertical components of the activityspecific lines of sight of the right eye and the left eye extend in afirst activity specific line of sight plane that is oriented at an angleθ_(v) to the normal line of sight plane, and horizontal components ofthe activity specific lines of sight of the right eye and the left eyeextend in a second activity specific line of sight plane that isoriented at an angle θ_(h) to the median plane.
 3. The protective shieldof claim 2, wherein at least one of θ_(h) or θ_(v) is at least 10degrees.
 4. The protective shield of claim 3, wherein at least one ofθ_(h) or θ_(v) is at least 15 degrees.
 5. The protective shield of claim3, wherein both θ_(h) or θ_(v) are at least 5 degrees.
 6. The protectiveshield of claim 3, wherein θ_(h) is about 15 degrees, and θ_(v) is about0 degrees.
 7. A shield for mounting on a protective helmet in an as wornorientation, the shield comprising; a one piece arcuate lens thatextends across and protects at least eyes and nose of a wearer when thelens is mounted to the protective helmet in the as worn orientation,such that a normal straight ahead line of sight extends through the lenswhen the lens is mounted in the as worn orientation and an apex of thelens is located at a forwardmost point of the lens or on a virtualextension of the lens; and wherein the optical axis extendssubstantially parallel to an activity specific line of sight of both theright eye and the left eye, and closer to the activity specific line ofsight of either the right eye or the left eye.
 8. The shield of claim 7,wherein the apex is at least about 10 mm below the normal straight aheadline of sight.
 9. The shield of claim 7, further comprising a verticalapex line through the apex in the as worn position, wherein the opticalcenter line extends through the optical center substantially on thevertical apex line.
 10. The shield of claim 7, wherein the activityspecific line of sight is displaced to one side of, and above or below,the normal line of sight.